1. Field of the Invention
The present invention pertains, in general, to a magnetic recording medium and, more particularly, to a high density magnetic recording medium including CoCrPt/Ti and fine grains, which has a uniform local coercivity distribution and grain size distribution, and a method of manufacturing the same.
2. Description of the Related Art
Currently, a thin film-shaped medium is usually used as a hard disk, and it is important to reduce the noise property amplified during amplifying a recording and a playback signal when a magnetic recording medium for the hard disk is used to realize a high density magnetic recording. In particular, grains in a magnetic layer must be fine and their sizes must be uniform so as to reduce a transition noise occurring by an interaction between the bits in transition regions between the bits, and the grains must be magnetically separated from each other to reduce an exchange coupling between the grains.
In the case of a perpendicular magnetic recording, the magnetic recording medium must secure thermal stability in a high density region, squareness of an M-H loop must approach 1, and its coercivity must be high in an allowable range of a recording sensitivity to stabilize stored information because the coercivity is an important factor functioning to prevent recorded information from being lost by neighboring magnetic fields. Furthermore, the degree of the perpendicular orientation of the magnetic recording medium must be very high, and local magnetic property of the magnetic recording medium must be uniform to realize the high density magnetic recording.
A CoCr alloy-based thin film has been most actively studied for utilizations as a perpendicular magnetic recording medium. A Co molecule having a hcp structure is a ferromagnetic substance, and has uniaxial crystalline magnetic anisotropy along a c-axis. When Cr is added to the Co molecule, the resulting mixture has high perpendicular magnetic anisotropy due to the uniaxial crystalline magnetic anisotropy improved by Co. Further, a composition segregation at interfaces between the grains caused by nonmagnetic Cr weakens an exchange interaction between the grains, thereby a medium noise which is one of problems occurring in regenerating information is reduced, and the perpendicular orientation of the columnar grains is improved. Accordingly, the CoCr alloy-based thin film has been continuously studied as a material of the high density magnetic recording medium with perpendicular magnetic anisotropy.
However, the CoCr binary alloy thin film has a limit in sufficiently increasing coercivity, improving the perpendicular magnetic anisotropy, and reducing the medium noise so as to realize the high density perpendicular magnetic recording medium. Accordingly, a CoCr binary alloy thin film including a third element has been developed.
Of various CoCr alloy thin films including the third element, CoCrPt alloy thin film has a relatively high coercivity and relatively large crystalline magnetic anisotropy in comparison with other CoCr-based alloy thin films, thus a recording medium including the CoCrPt alloy thin film has high output, strong perpendicular orientation, and large perpendicular magnetic anisotropy. Accordingly, many studies have been made of the CoCrPt alloy thin film.
However, the CoCrPt alloy thin film is disadvantageous in that when a great amount of Pt is added to the CoCrPt alloy thin film, the composition segregation at interfaces between the grains is weakened and the exchange interaction between the grains is strengthened even though the CoCrPt alloy thin film has a magnetic property suitable as the high density magnetic recording medium, thereby the medium noise is undesirably increased. Accordingly, many studies have been made to add a fourth element to the CoCrPt alloy thin film or to layer a underlayer including a nonmagnetic material on the CoCrPt alloy thin film to reduce the sizes of the grains, reduce the exchange interaction between the grains, and reduce the medium noise, thereby realizing the magnetic recording medium having low noise property as well as high coercivity, magnetic anisotropy, and squareness ratio.
For example, U.S. Pat. No. 5,049,451 (Lal, Brij B et al.) discloses a magnetic recording medium having CoCrTaPt, which includes CoCr, 3 to 20 atom % Pt, and 2 to 10 atom % Ta, thereby having low medium noise as well as high coercivity and squareness ratio. Furthermore, U.S. Pat. No. 4,929,514 (Natarajan, Bangalore R. et al.) proposes a recording medium, in which a magnetic layer including 60 to 80 atom % Co, 5 to 20 atom % Cr, and 1 to 20 atom % Pt is layered on a underlayer including Cr or a Cr alloy, thereby having high coercivity and low medium noise.
However, the prior arts about the magnetic recording medium including CoCrPt suggest no microscopic observation of magnetic properties. For example, a local coercivity distribution greatly affects to determine a magnetic domain inverse behavior of a thin film, thus the local coercivity distribution must be observed so as to realize the high density magnetic recording medium. However, in the prior arts, no study of the local coercivity distribution is made because of technical limits.